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Round-up of the latest literature on ophthalmological matters

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01 February 2014, at 12:00am

Use of ultrasound in the diagnosis of ocular diseases in cats, dogs and horses 

Nicolin Gallhoefer and others, University of Zurich, Switzerland 

Ultrasonography is potentially a very useful method for investigating ocular diseases because it is safe, readily available, cost effective, non-invasive and may be performed without sedation. However, most published accounts in the veterinary literature have involved tentative diagnoses and there is little information on their accuracy. 

The authors assessed the diagnostic value of ultrasound examination by comparing the results with those of histological analyses following the removal of the diseased organ. A total of 116 eyes from 113 animals of three domestic species were examined. There was good agreement between the ultrasound and histological findings in those animals with intraocular neoplasia but those cases with haemorrhagic or inflammatory changes were frequently misdiagnosed as neoplasia on ultrasound examination. Meanwhile, retinal detachment was not detectable using ultrasound in more than one-third of cases in which that diagnosis was achieved on histological examination. 

Journal of the American Veterinary Medical Association 243 (3): 376-388.

Ocular emergencies in the dog and cat 

Georgina Gent, Davies Veterinary Specialists, Hertfordshire

Ocular emergencies may involve any one of a range of conditions requiring urgent action to avoid severe impairment of the patient’s vision or loss of the globe itself. In the first of a two-part series, the author discussed the assessment and management of globe proptosis, acute glaucoma, lens luxation and removal of a corneal foreign body. In the second paper, she offers advice on the emergency management of deep or melting corneal ulceration, corneal laceration, lid lacerations, severe ocular and adnexal contusions and sudden onset blindness. 

Companion Animal 18 (6): 271-176; 18 (8): 386-389.

Chromatic pupil light reflex testing in the diagnosis of retina and optic nerve conditions

Sinisa Grozdanic and others, Animal Eye Consultants, North Liberty, Iowa 

Pupillary light reflex testing is well- established as a fast, non-invasive method for detecting retina and optic nerve diseases. But recent advances in understanding of the physiology of light perception have encouraged the use of specific wave lengths rather than white light sources used in such tests. The authors assess the use of chromatic pupillary light reflex analysis using red and blue light and electroretinography in canine patients with a range of ocular conditions. Their findings suggest that evaluation of the chromatic pupil light reflex is a potentially effective strategy for both the diagnosis and differentiation of retina and optic nerve diseases. 

Veterinary Ophthalmology 16 (5): 329-340.

Risk factors for the development of corneal ulcers after non-ocular surgery

Young-Woo Park and others, Seoul National University, South Korea 

Reduced tear production and blood flow changes may both occur in the eyes of patients undergoing general anaesthetic and may explain occasional incidents of post-operative corneal ulcers. The authors evaluate the prevalence and risk factors involved in the development of corneal ulcers in 14 dogs compared with 718 healthy controls. The duration of anaesthesia was significantly longer in those dogs that developed corneal ulcers and the number of medications received and procedures performed was significantly higher. Dogs with a small skull and those undergoing neurosurgery were also more likely to develop such complications.

Journal of the American Veterinary Medical Association 242 (11): 1,544-1548.

Prevalence of uveal cysts and pigmentary uveitis in Golden Retrievers 

Wendy Townsend and Kara Gornik, Purdue University, Indiana 

Pigmentary uveitis is a condition in Golden Retrievers involving the deposition of pigment on the anterior aspect of the lens capsule. It was first identified in the US in 1996 and appears well established within the breed in that country and it has now also been reported in a home-bred dog in Britain. The authors investigate the prevalence of the condition in Golden Retrievers in three Midwestern states. They found evidence of pigmentary uveitis and uveal cysts in 5.5% and 34.3% respectively of dogs of this breed in Illinois, Indiana and Michigan, a significantly higher prevalence than suggested by previous studies.

Journal of the American Veterinary Medical Association 243 (9): 1,298- 1,301. 

Technique for the surgical replacement of a prolapsed third eyelid gland 

Amy Rankin, Kansas State University

Cherry eye, a prolapsed gland, is the most common disorder of the third eyelid in dogs, occurs most commonly in young dogs of the American cocker spaniel and English bulldog breeds. The author describes a modified Morgan pocket technique for the surgical treatment of this disorder. In the original procedure, a conjunctivectomy is performed and the suture knots are buried but in the modified technique, the former procedure is eliminated and the knots placed on the anterior surface of the third eyelid to prevent possible trauma to the cornea. The main advantage of the modified technique is that it allows the third eyelid to move normally post-operatively.

Veterinary Medicine 108 (10): 462-468.

Multiple congenital ocular anomalies syndrome in Shetland ponies 

Johanna Premont and others, University of Liege, Belgium 

Equine multiple congenital ocular anomalies syndrome is a condition associated with the silver phenotype in various breeds. The authors describe the phenotypic and genotypic characteristics of MCOA in a family of silver-coated Shetland ponies and a related Deutsches Classic pony in Belgium. A 20-year-old stallion had a thickened iris, temporal retinal atrophy and bilateral iridocillary and peripheral retinal cysts while four related females had more severe abnormalities including corneal globosa, iridocorneal adhesions, miosis, hypoplastic granula iridica and poorly responsive pupils. The stallion was heterozygous for the silver mutation whereas the females were all homozygous.

Equine Veterinary Education 25 (11): 550-555.

Histopathological findings in canine eyes removed due to glaucoma 

Anthony Alario and others, Tufts University, Massachusetts

Primary lens displacement is a spontaneous condition caused by an inherited defect in the lens zonules and will often lead to secondary glaucoma. The authors investigated the histological changes seen in 13 eyes from 12 patients removed due to PLD and secondary glaucoma. In each case there was evidence of inflammation involving the iris and cleft, with mononuclear and melanophagic infiltration of the cleft. It is suggested that an inflammatory reaction directly or indirectly related to melanin release may obstruct the outflow pathways ultimately leading to glaucoma and loss of vision and that dogs in the early stages of the process may be treated with topical steroids.

Veterinary Ophthalmology 16 (1): 34-41. 

Efficacy of peribulbar anaesthesia in dogs undergoing phacoemulsification 

Jaesang Ahn and others, Seoul National University, South Korea

Analgesia during cataract removal will normally be achieved through the systemic administration of opiates and/or non-steroidal anti- inflammatory drugs. As both groups of analgesics may produce significant adverse effects, peribulbar anaesthesia (a sub-Tenon injection of lidocaine) has been suggested as an alternative option. The authors investigated the effects of this treatment on the extraocular muscles, pupil dilation and intra-operative and post-operative analgesia in dogs undergoing phacoemulsification. Experimental procedures in 14 beagles showed that the method provided effective analgesia, while also producing akinesia of the extraocular muscles and inducing mydriasis.

American Journal of Veterinary Research 74 (8): 1,126-1,132.

Changes in understanding of the pathogenesis of equine corneal stromal abscesses 

Michala de Linde Hendriksen and others, University of Florida 

Thirty years ago stromal abscesses were considered to be a condition mainly affecting horses in subtropical regions, associated with bacterial infection, recurrent uveitis, corneal microtrauma and corneal foreign bodies. Now the condition is recognised as a problem in temperate climates and is considered to be due to fungal inoculation of the anterior corneal stroma. The authors review the developing perceptions of the pathogenesis and resulting changes in the treatment of corneal stromal abscesses over the past three decades. They note that current treatments now have a high expectation of success in speeding healing and preserving sight. 

Equine Veterinary Education 25 (6): 315- 323.

Degree and duration of corneal anaesthesia with topical oxybuprocaine hydrochloride

Jean-Yves Douet and others, National Veterinary School, Toulouse, France

Oxybuprocaine hydrochloride was developed for use in human ophthalmological surgery to enable rapid anaesthesia of the ocular surface. The authors investigate the duration and quality of anaesthesia achieved with a 0.4% solution of this compound in healthy dogs, when compared with the established topical anaesthetic tetracaine. Measurements of the corneal touch threshold showed that the two topical anaesthetics were similarly effective in reducing corneal sensitivity but the oxybuprocaine solution was less irritating to the conjunctivae than tetracaine.

American Journal of Veterinary Research 74 (10): 1,321-1,326.

Systemic hypertension and hypertensive retinopathy following PPA overdose 

Jennifer Ginn and others, University of Wisconsin 

Phenylpropanolamine (PPA) was the principal ingredient in some over-the- counter decongestant and appetite suppressant products that were withdrawn from the US market in 2000. The authors describe the clinical findings in an incident involving a four-year-old spayed female Labrador which ate 40 to 50 tablets containing the drug. On presentation within four hours of eating the tablets, it had clinical signs of anxiety, piloerection, mucosal ulceration, cardiac arrhythmia and mydriasis. It was also found to have ventricular tachycardia and severe systemic hypertension and there was hyphaemia and retinal detachment in both eyes. Treatment with phenoxybenzamine, sotalol and esmolol resolved the cardiac abnormalities and the hypertension was controlled with nitroprusside. 

Journal of the American Animal Hospital Association 49 (1): 46-53.